The answer is The increased opposition to war.
Nixon was not popular with his foreign policy of war to fight communists. During his term, people held numerous strikes that showed that the people were against its implementation. They don't want numerous soldiers to get involved and suffer. They also don't want people from foreign lands to lose their lives because of this.
Because chine has recently started industrializing and the usa uses them for cheeper labor and industry
The name for this idea is "Domino Effect" - this is a theory that says that if one country falls to Communism the neighboring countries would also fall to Communism, much like pieces of Dominos fall when a neighboring piece fell.
This theory was important in the Foreign politics of the US during the cold war.